The making of a succession of bags from a web of sheet material by forming the web about a mandrel, advancing the web along the mandrel to sealing means to simultaneously form a seal transversely of the tube which constitutes in part the top of one bag and the bottom of the succeeding bag is old in the art. In accordance with the procedure followed by most bag manufacturers, heat sealable sheet material is employed and the sealing instrumentalities are provided with jaws containing heating elements which are brought together to form the seal. Cutting elements may also be embodied in the jaws or associated therewith to sever the tube within the area of the seal. Heat sealable material is expensive and so it is desirable to substitute therefor where the specific qualities of the heat sealable material are not required, sheet material which is not heat sealable and to apply a heat activatable adhesive thereto at intervals corresponding to the length of the bags to be made. Feeding the adhesive pre-printed web to the instrumentalities gives rise to problems because a very small error in the feed will multiply in a long length of web to displace the adhesive out of registration with the sealing instrumentalities with the result that no seal will be formed. Attempts to control the feed by printing indicia on the web at predetermined spacing in relation to the adhesive to control the feed by means of the indicia to intermittently advance the feed slightly more than the bag length and then slightly less than bag length to average out the error in spacing has been tried. The method is not completely successful and the control required is unusually complicated. The apparatus herein illustrated is designed to achieve control directly from the passage of the bars of adhesive relative to a detector and so without accumulation of errors which are inevitably introduced by the use of indicia.